In the treatment of patients with certain kinds of cancer or rheumatoid arthritis, methods are known in which radioactive particles are introduced intravascularly to a tumor site (radioembolization) or locally into the synovial fluid in a joint in order to trap the radioactive particle at a particular site for its radiation effect. Similar methods are used for imaging parts of the body, organs, tumors, and so forth.
According to this technique, a quantity of the radioactive particles are injected into a localized area of the patient to be imaged and/or treated. For imaging, gamma emitting materials are commonly used to label carriers that provide imaging of a tissue area, tumor or organ. Some of these carriers have a specific affinity for certain binding sites or biochemical targets allowing target specific or location specific uptake of the labelled carrier.
Radiological imaging of various tissues in the human body is commonly accomplished using Technetium-99m, typically by single photon emission computed tomography (SPECT). 99m-Tc is a well-known radioactive isotope used for radiodiagnostics and imaging such as SPECT. It emits detectable low level 140 keV gamma rays, has a half-life of 6 hours and decays to Tc-99 in 24 hours (93.7%). It is used for imaging and function studies of the brain, myocardium, thyroid, lungs, liver, gallbladder, kidneys, bone, blood, and tumors. It is reported to be used in over 20 million diagnostic nuclear medicine procedures each year. Positron emission tomography (PET) employs radionuclides that emit positrons, a beta-like nuclear particle that travels a few millimetres from its nucleus, collides with an electron leading to annihilation resulting in creating two photons of 511 KeV that travel in 180° opposite direction. The PET imaging system captures and registers the photons arising from the collision precisely at the same time thereby providing exceptional imaging sensitivity. PET imaging has become a valuable diagnostic imaging procedure, particularly in the oncology area and it has been reported that in the US approximately two million PET scans are performed annually. Radioisotopes commonly employed for PET imaging include fluorine-18 (18F) that has a half-life of 109.8 minutes and gallium-68 (68Ga) that has a half-life of 68 minutes.
Targeted radiation therapy using microparticles or microspheres is also a well-developed field radioisotope therapy. Radionuclides such as Yttrium-90 and Holmium-166 are commonly used radioactive beta emitters in microsphere radiotherapy. Polymer microspheres such as albumin, poly-lactic acid derivatives, and so forth, and glass microspheres, are both generally known in the medical arts for use in delivering both pharmaceuticals and radiopharmaceuticals to specific tissue sites. These microspheres are usually provided preloaded with a single radionuclide and so lack the flexibility to control dose or radionuclide depending on the patient's needs. Further, when radio micro particles are prepared in bulk, off-site by third party providers, the selection of radionuclide available for use may be limited, by the time involved in preparation and delivery.
However, a need remains for a radioactive microparticle for delivery of one or more radiopharmaceuticals and which have characteristics which will permit the microparticles to be suitable for injection into a patient for localized imaging or therapy.